tropical ecosystems in particular can be anywhere
from moderately to severely affected.
El Niños tend to alternate with another climatic
phenomenon that produces largely the opposite effects
called La Niña. Like El Niño, La Niña systems begin when
normal trade winds are altered. In this case however, the
westward trade winds gain abnormal strength and move
further westward than normal, carrying warm surface
water toward Asia. This creates enhanced upwelling of
colder, deeper, more nutrient-rich water along the South
American coast. Because the colder waters evaporate
more slowly, rain is reduced and drought may result. La
Niñas have followed El Niños after the 1982– 83, 1986–
87, 1994– 95, and 1997– 98 El Niños.
Ecologists realize that ENSO events cause short-
term but nonetheless significant perturbations in
ecosystems including the lowland tropics. A major El
Niño affected Barro Colorado Island (BCI) in Panama
during 1982– 83. One of the most dramatic effects of
that El Niño was the failure of trees to produce fruit
during the second of two fruiting seasons. The failure of
the fruit crop resulted in a cascade of severe impacts on
various animals. Researchers on the island noted that
normally wary species such as the Collared Peccary,
coatis, Baird’s Tapir, and Kinkajou made regular visits
to the laboratory area where food had been put out
for them. Some of these animals appeared emaciated,
obviously under stress from lack of food. Robin Foster,
a researcher at BCI, wrote:The spider monkeys, which normally visit the
laboratory clearing at least once every day, now
launched an all- out assault on food resources inside
the buildings, learning for the first time to open
doors and make quick forays to the dining room
table, where they sought bread and bananas, ignoring
the meat, potatoes, and canned fruit cocktail, and
brushing aside the startled biologists at their dinner.Dead animals, Foster wrote, were also encountered
far more frequently than usual:Plate 2- 2. This photo was taken in January 2016, at extreme low water in a Panamanian river during a drought attributed to the
most severe El Niño/Southern Oscillation event on record. Photo by John Kricher.
36 chapter 2 why it is hot, humid, and rainy in the tropics